Abstract: Apparatus (1) for performing an electrical test on a cable (3) used in local area networks (LAN's). A source (37) produces electrical signals transmitted through the cable. A resistance circuit (43) is interposed between the source and the cable. The amount of resistance interposed by the resistance circuit is adjusted using an adjustment circuit (67). A sensor (71) senses a characteristic of the signal and determines when that characteristic has a value representing an inpedance match between the source and the cable. The sensor circuit provides a command to the adjustment circuit to thereafter maintain the point of adjustment at which the impedances are matched.